FOREST STRUCTURE AND REGENERATION DYNAMICS OF PODOCARP/HARDWOOD FOREST FRAGMENTS, BANKS PENINSULA, NEW ZEALAND A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Applied Science at Lincoln University by Nancy Willems Lincoln University 1999 11 Abstract of a thesis submitted in partial fulfilment of the requirements for the Degree of M.AppI.Sc. FOREST STRUCTURE AND REGENERATION DYNAMICS OF PODOCARP/HARDWOOD FOREST FRAGMENTS, BANKS PENINSULA, NEW ZEALAND. by Nancy Willems Although species maintenance in small forest fragments relies on successful regeneration and recruitment, few studies have examined the effects of fragmentation on regeneration processes. New Zealand's podocarp species rely on large disturbance openings operating across a vegetated landscape to stimulate regeneration. Clearance of vegetation that results in small fragments of forest removes regeneration opportunities for podocarps by destroying the intact vegetation mosaic, and as a result may exclude disturbances of the scale necessary for podocarp regeneration. Fragmentation alters the disturbance regime of the landscape, with important implications for the regeneration of podocarps on Banks Peninsula. The four remaining lowland podocarp-hardwood fragments on Banks Peninsula were sampled to determine the structure and regeneration patterns of podocarps and to assess their long term viability. Density, basal area, and size and age class distributions were used to examine current composition, and in conjunction with spatial analysis, to identify past regeneration patterns and infer likely future changes in composition and population structure. Podocarp size and age class structures for three of the four fragments were characteristically even-sized and relatively even-aged (eg; Prumnopitys taxifolia c. 350 to 600 years), with little or no regeneration for approximately the last 200 years (old-growth fragments). Regeneration of the current podocarp canopy in the old-growth fragments may have been stimulated by flooding. 111 The fourth younger fragment showed much more recent regeneration with Prumnopitys taxifolia, Podocarpus totara and Dacrycarpus dacrydioides mostly 80-160 years old, and substantial populations of seedlings and saplings, probably as a result of anthropogenic fire. In the absence of major disturbance the podocarp component in forest fragments on Banks Peninsula is likely to decline with composition shifting towards dominance by hardwood species. There is some evidence to suggest that canopy collapse will stimulate some podocarp regeneration within the fragments, however it appears to be unlikely that podocarps will persist on Banks Peninsula indefinitely within the fragments studied. There is an urgent need for more quantitative research in New Zealand fragmentation literature, and a need for more emphasis on processes. Banks Peninsula offers potential for a more landscape scale approach in forest management, and the maintenance of regenerating scrub in pockets about the Peninsula may offer the regeneration opportunities for podocarps that are lacking within protected fragments. My study took a quantitative approach in examining the effects of forest fragmentation on the demographics of podocarps and compositional change in forest fragments on Banks Peninsula. Keywords: Composition, Dacrycarpus dacrydioides, disturbance, forest structure, fragments, hardwood, podocarp, Podocarpus fofara, Prumnopitys faxifolia, regeneration. iv Table of Contents PAGE Abstract ii Table of Contents iv List of Tables vii List of Figures ix List of Plates xi CHAPTER 1: INTRODUCTION 1 1.1 Podocarp Regeneration 2 1.2 The Role of Disturbance 5 1.3 Fragmentation 8 1.4 Altered Disturbance Regimes 14 1.5 The Combined Effects of Fragmentation and Changed Disturbance Regimes 17 Hypotheses 18 Specific objectives 19 CHAPTER 2: STUDY AREA AND SITE DESCRIPTIONS 20 2.1 Study Area: Banks Peninsula 20 2.1.1 Geology 21 2.1.2 Climate 21 2.1.3 Vegetation 22 2.1.5 European Settlement and Land Use 23 2.2 Site Descriptions 24 2.2.1 Okuti Valley Reserve 25 Vegetation 25 Conservation Value 25 Threats to Reserve 26 2.2.2 Hay Reserve 26 Vegetation 26 Conservation Value 27 Threats to the Reserve 27 v Table of Contents cont. .. PAGE 2.2.3 Prices Valley Covenant 27 Vegetation 28 Conservation Value 29 Threats to the Reserve 29 2.2.4 Kaituna Valley Reserve 30 Vegetation 30 Conservation Value 30 Threats to the Reserve 30 CHAPTER 3: METHODS 32 3.1 Plot Design and Placement 32 3.2 Data COllection 34 3.3 Forest Composition and Structure 35 3.4 Increment cores 36 3.6 Association tests 37 CHAPTER 4: RESULTS 38 4.1 Okuti Valley Reserve 38 4.1.1 Forest Composition 38 4.1.2 Size and Age Structures 40 4.1.3 Spatial patterns ofestablishment 47 4.1.4 Stand dynamics 52 4.2 Hay Reserve 54 4.2.1 Forest Composition 54 4.2.2 Size and Age Structures 56 4.2.3 Spatial patterns ofestablishment 60 4.2.4 Stand dynamics 62 4.3 Prices Valley Covenant 63 4.3.1 Forest composition 63 4.3.2 Size and Age Structures 64 vi Table of Contents cont. .. PAGE 4.3.3 Spatial Patterns ofEstablishment 67 4.3.3 Stand Dynamics 71 4.4 Kaituna Valley Reserve 72 4.4.1 Forest Composition 72 4.4.2 Size and Age structures 73 4.4.3 Spatial patterns ofestablishment 75 4.4.4 Stand Dynamics 77 4.5 Comparison of Reserves 78 CHAPTER 5: DISCUSSION 79 5.1 Podocarp Regeneration Dynamics in Forest Fragments 82 5.2 Hardwood Regeneration Dynamics in Forest Fragments 88 5.3 Possible Future Compositions 90 In the absence of major disturbance 91 Progressive canopy collapse 93 In the event of amajor disturbance 95 5.4 Implications for Future Research and Management 95 5.5 Conclusions 97 ACKNOWLEDGEMENTS 98 REFERENCES 99 APPENDICES 105 Appendix 1: Density and basal area of podoearps and hardwoods ~ 5 em dbh 105 Appendix 2: Podoearp and hardwood seedling and sapling densities « 5 em dbh) 109 Appendix 3: Spatial Analysis Correlograms 112 Okuti Valley Reserve 112 Prices Valley Covenant 118 vii List of Tables TABLE PAGE 2.1 Site summaries (Kelly, 1972) 24 4.1 Density and basal area of podocarps and hardwoods ~ 5 cm dbh, Okuti Valley 39 Reserve. 4.2 Seedling and sapling densities « 5 cm dbh) of podocarps and hardwoods (ha-1), 40 Okuti Valley Reserve. 4.3 Age range estimates made by Ebbett (1998) from the terrace area of Okuti 44 Valley Reserve. Corrections for age to coring height were made for these estimates (Ebbett, 1998). There was some overlap between Ebbett's plots and those laid out for this study, however, only a few individual trees were aged in both studies. 4.4 Significant results of spatial association tests (p ~ 0.05), Okuti Valley Reserve, 50 Plot 2. Numbers following backslash indicate the distance of the associations in metres. 4.5 Significant results of spatial association tests (p ~ 0.05), Okuti Valley Reserve, 52 Plot 3. Numbers following backslash indicate the distance of the associations in metres. 4.6 Canopy cover estimates for quadrats with and without podocarp seedlings and/or 52 saplings, Okuti Valley Reserve. 4.7 Density and basal area of podocarps and hardwoods ~ 5 cm dbh, Hay Reserve. 55 4.8 Seedling and sapling densities « 5 cm dbh) of podocarps and hardwoods (ha-1), 55 Hay Reserve. 4.9 Canopy cover estimates for quadrats with and without podocarp seedlings and/or 62 saplings, Hay Reserve. 4.10 Density and basal area of podocarps and hardwood ~ 5 cm dbh, Prices Valley 64 Covenant in a 0.9 ha plot. 4.11 Seedling and sapling densities « 5 cm dbh) of podocarps and hardwoods (ha-1), 64 Prices Valley Covenant. 4.12 Significant results of spatial association tests (p ~ 0.05), Prices Valley Covenant. 70 Numbers following backslash indicate the distance of the associations in metres. V111 List of Tables cont... TABLE PAGE 4.13 Canopy cover estimates for quadrats with and without podocarp seedlings and/or 70 saplings, Prices Valley Covenant. 4.14 Density and basal area of podocarps and hardwoods (;::: 5 cm dbh), Kaituna 73 Valley Reserve, in a 0.6 ha plot. 4.15 Seedling and sapling densities « 5 cm dbh) of podocarps and hardwoods, 73 Kaituna Valley Reserve. 4.16 Canopy cover estimates for quadrats with and without podocarp seedlings and/or 77 saplings (ha-1), Kaituna Valley Reserve. 4.17 Summary table of reserve characteristics. Densities are given in stems ha-1, 78 basal areas in m2 ha-1, and ages in years. Percentage of total is given in brackets. List of Figures FIGURE PAGE 1.1 Clementsian model of succession and climax (Clements, 1916). 2 1.2 Cyclic regeneration (adapted from Cameron, 1955). 4 2.1 Location and study sites, Banks Peninsula, New Zealand. 1- Kaituna 20 Valley Reserve; 2- Prices Valley Covenant; 3 - Okuti Valley Reserve; 4 - Hay Reserve. 3.1 Basic plot design. Numbers and letters refer to 5 mx 5 mquadrats (Eg; 32 A1, B1.....) for recording data. Seedlings and saplings were sampled in every fourth quadrat, marked #. Solid lines indicate 5 mwide strips, and dotted lines mark the extent of 5 mx 5 mquadrats within each strip. Plots were made as large as possible while avoiding streams, fences, standing water and edges. 3.2 Reserve maps showing major features and plot placement. A- Kaituna 33 Valley Reserve; B- Hay Reserve; C- Prices Valley Covenant; D- Okuti Valley Reserve. 4.1 Size class frequency distributions, Okuti Valley podocarps. sd = 42 seedlings, s = saplings. 4.2 Age vs diameter in Okuti Valley Reserve. Prumnopitys taxifolia n=4 (e), 43 Dacrycarpus dacrydioides n=19 (_), Podocarpus totara n=14 C"). 4.3 Size class frequency distributions for Kunzea ericoides, Okuti Valley 45 Reserve. 4.4 Hardwood size class frequency distributions, Okuti Valley Reserve (~5 46 cm dbh). 4.5 Size class frequency distributions for Cyathea dealbata, Okuti Valley 47 Reserve.